This invention concerns a molding apparatus and method and, more particularly, a method of molding an elastomeric member of generally elongated shape, and having wire mesh reinforcing sleeves molded into the ends of the member, the ends having a shape which conforms to a specialized profile.
There has heretofore been proposed and described energy storage devices for regenerative braking systems which involve the use of torsionally stressed elongated elastomeric members to store the mechanical energy normally dissipated in the braking of vehicles.
Such system and devices are described in U.S. Pat. Nos. 4,246,988; 4,305,489; 4,310,079; and 4,319,655. In order to improve the energy storage capacity and fatigue life of the elastomeric member, there is disclosed in U.S. Pat. No. 4,333,553 an arrangement whereby the elastomeric member or members are prestressed under tension in order to reduce the tendency for knotting under high torsional stresses. Such prestressing involves considerable elongation of the elastomeric member over its relaxed state.
As described in co-pending application, Ser. No. 469,618, filed on 2/25/83, and assigned to the same assignee as the present application, it is highly desirable that the stretched elastomeric member have a substantially uniform diameter in order that the member may be disposed within a minimum diameter housing in the interest of conserving space.
There is described in the aforementioned copending application, a configuration of the elastomeric member in which this is achieved in a simple but effective manner.
This arrangement involves a particular profiling of the ends of the elastomeric member and also involves the molding of wire mesh sleeves into the ends of the elastomeric member.
The elastomeric members are subjected to relatively high torsional stresses; and for use in regenerative braking systems, the service life of the elastomeric member is an important consideration since many thousands of cycles of torsional stressing should desirably be able to be undergone without failure.
It has been found that any aberrational feature on the surface of the member produces an undesirable stress concentration, tending to lead to early fatigue failure of the member in service.
Several of such irregularities or aberrational features may be created during the process of molding the elastomeric member.
The elastomeric member for such applications has advantageously involved the use of a natural rubber compound or synthetic having similar properties which is molded into its final shape by application of pressure and heat while being confined within a mold cavity.
The traditional art of molding involves the use of split mold halves, with a central sprue or series of sprues, and often a series of relief ports.
The expansion of rubber material into a sprue opening or a mold seam and/or the shrinkage of material after cooling produces surface protuberances or depressions which act as stress concentrators.
In addition, the use of a split compression-type mold does not ensure full fill of the mold cavity, also creating the possibility of surface voids.
The elimination of such surface features as by conventional molding techniques has been difficult to achieve.